Field of the Invention
The present invention relates to an apparatus, system and method for logging wells to obtain well information and to improve directional steering of bores drilled to a targeted geologic formation. More specifically, the present invention relates to a re-usable antenna assembly including a sacrificial wear member to protect an element within the antenna assembly.
Background of the Related Art
Well logging devices are included in well logging assemblies that are made up into a drill string and lowered into a drilled earthen bore to detect conditions in a geologic formation penetrated by the bore. The detected conditions generally indicate the presence and/or absence of certain recoverable fluids that reside in the pores of the rock that makes up the geologic formation. Well logging assemblies include devices that generate a signal aimed at and transmitted into a geologic formation of interest adjacent to the bore in which the well logging assembly is deployed. Well logging assemblies also include devices that sense or detect a signal reflected by or returned from an adjacent geologic formation of interest. Some well logging assemblies include a first well logging device to induce an electrical current to flow within the geologic formation of interest and a second well logging device to measure the resulting current flow in the formation. The measurement of the resulting current flow enables the determination of the electrical resistivity of materials residing within pores of the formation of interest. For example, a high resistance to current flow generally indicates that a non-conductive fluid, such as hydrocarbon oil or gas, resides in the pores of the formation, and a low resistance to current flow generally indicates that a conductive fluid, such as brine or water, resides in the pores of the formation.
In some applications, the spacing of a first, signal-generating well logging device on a well logging assembly relative to a second, signal-detecting well logging device on the well logging assembly determines the depth of investigation; that is, the spacing between the first and second well logging devices determines the distance into the formation, and from the bore in which the tool is deployed, that is being investigated using the well logging devices. A greater separation of the first well logging device from the second well logging device provides a greater distance into the geologic formation from the bore that is investigated, and a lesser separation of the first well logging device from the second well logging device provides a lesser distance into the formation from the bore that is investigated.
It is advantageous to provide elements on a well logging assembly that protect the well logging devices assembled thereon without impairing the performance of the well logging devices. Antenna assemblies used in well logging may be used to both transmit a signal from a well logging assembly into the formation of interest, and also to receive a responsive signal from the formation of interest to the well logging assembly. These antenna assemblies generally require non-conductive elements either to provide a path through which a signal can pass and/or to provide an insulation barrier so that an electric potential can be applied across the non-conductive element of the well logging assembly. There is a tension between providing high-strength and durable elements, such as metal protective sleeves, to surround and protect well logging devices, and maintaining insulating elements to enable the well logging devices to function efficiently; that is to transmit and receive signals. Non-conductive materials that do not impair the function of the well logging device antenna may be subject to erosion and wear when used to protect well logging devices that are included in well logging assemblies.